This invention relates to the field of IP (Internet Protocol) networks and more specifically to a method and arrangement for decreasing the amount of data transferred when signalling in an environment of bandwidth restrictions.
TCP/IP (Transmission Control Protocol/Internet Protocol) Internet Protocol Suite is today a very commonly used protocol suite for communicating data and voice over IP networks. This protocol suite is optimised for wired connections, which have a relatively high transmission quality, a low latency and comparatively large bandwidth. However TCP/IP is not very efficient for transmitting data or voice over links with low bandwidth. Wireless links in e.g. mobile communication constitute examples of links with low bandwidth.
In the TCP/IP Internet Protocol Suite the TCP is responsible for breaking up the message to be transmitted into datagrams i.e. a collection of submessages, reassembling the datagrams into the original message at the other end of the communications network, resending anything that gets lost, and arranging the message parts in the right order. An alternative to TCP is UDP (User Datagram Protocol) which sends the datagrams without any control of whether the datagram has arrived or not. This protocol is commonly used when sending voice over IP. The IP is responsible for routing individual. IP does not specify how the datagrams are related to each other. In order to keep track of details such as source and destination port numbers, datagram sequence number, checksums and other control data, TCP/UDP attaches a header to each datagram and hands over a combined header + datagram to IP. IP then adds its own header to this xe2x80x9cTCP/UDP-header + datagramxe2x80x9d so that the resulting packet of data appears to be xe2x80x9cIP-header + TCP/UDP-header + datagram. In cases where the application is character-based, the headers can be 40 bytes or more long for each byte of data transferred. The words xe2x80x9cdatagramxe2x80x9d and xe2x80x9cpacketxe2x80x9d are often used interchangeably although xe2x80x9cdatagramxe2x80x9d is correctly defined as a unit of data, and what the protocol deals with. However in some cases the TCP/IP datagram may be broken up into smaller pieces (e.g. if the datagram is comparatively big ) and another header appended to each smaller piece or xe2x80x9cpacketxe2x80x9d
One way of solving the problem with bandwidth constraints is to decrease the amount of data to be transferred by means of so-called header compression.
In the past attempts have been made to develop specialised protocols which limit the overhead required in transmitting data over a local area network (xe2x80x9cLANxe2x80x9d) and to make use of certain inherent characteristics of a given network type to minimise the message overhead in a certain communication session. Message overhead is the header information, which is appended to the data portion of the message. Such header information is necessary to permit various portions of a network to keep track of the administrative and procedural tasks required to transfer data from one computer to another. One attempt to improve the efficiency of a protocol is the header compression methodology outlined in xe2x80x9cCompressing TCP/IP headers for low-Speed Linksxe2x80x9d by V. Jacobsen, Network Working Group Request for comments: 1144, February 1990.
In this methodology the sender and the receiver keeps track of active connections. The receiver keeps a copy of the header from the last packet received from each connection. Compression is obtained by transferring only a small ( less than =8 bit) connection identifier of the part of the header that is constant over the connection together with the part of the header that has been changed. The receiver fills in the constant part from the saved header.
European Patent Application No. 0701354 describes an alternative way of using TCP/IP header compression. More specifically it shows a method for using header compression over X.25 networks.
When sending voice over IP over a radio link it is very important to make efficient use of the available bandwidth and spectrum. Sending voice over IP requires some signalling to set-up the connection and for monitoring the connection. This means further consumption of bandwidth. The same problem arises for all links with bandwidth constraints when packet based services are used, and which require signalling for establishing a connection e.g. satellite communications, cellular communications and wireless LAN. The header compression methodology is not optimised for this type of traffic and not sufficiently efficient.
Signalling traffic is different from other traffic in following aspects:
Signalling messages are for set-up, release and control of a connection.
Signalling messages are frequently transferred, often with a predictable frequency, during often used procedures, e.g. call-setup and call-release
In some cases the signalling message is repeated, e.g. so-called keep-alive messages.
These characteristics for signalling messages motivates a new model for compression of redundant information, optimised for this kind of traffic. The present invention proposes a solution to this problem.
The present invention deals with the problem with packet based services consuming considerable bandwidth over links with shortage of bandwidth.
In situations with bandwidth constraints and where signalling is required for establishing the connection, e.g. voice over IP over radio links, the performance of the communication can be degenerated due to heavy signalling.
The object of the present invention is thus to reduce the amount of information in the signalling and thus save bandwidth.
The aforesaid problem is solved by means of a communication system wherein a signalling message is replaced by an indicator.
The following scenario of transferring a signalling message describes the inventive concept of the present invention.
After receiving a signalling message in a first node the signalling message is identified. The signalling message is replaced by an indicator, under usage of information from the identification, which indicator is transferred to a second node.
The second node restores the signalling message using the indicator.
An advantage of the present invention is that less information need to be transferred when transferring a signalling message.
Another advantage is that the whole signalling message, header and payload can be reduced by the present invention.
Another advantage is that less bandwidth is required when transferring a signalling message which means that the bandwidth can be used for other purposes e.g. user data traffic and other signalling messages.
Yet another advantage is that that the invention makes it possible to use packet based services which require signalling for establishing a connection where it before was impossible due to too low bandwidth.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.